Method of Unit Level Liquid Crystal Display Device Assembly Process for Liquid Crystal on Silicon

ABSTRACT

The present invention provides a method of unit level liquid crystal display device assembly process for liquid crystal on silicon. It starts with sawing silicon wafer and ITO glass substrate. Then good silicon dies and ITO glass dies will be picked and transferred to separate carriers. Alignment layers will respectively be coated on each silicon die and ITO glass die after cleaning. Then there are two options for the following steps. In method one, silicon die and ITO glass die lamination comes after coating frame adhesive. Then frame adhesive is cured. The liquid crystal will fill the cell and then seal the fill port. Die mounting, wire bonding and encapsulation will come along with external ITO connection to call it an end. In method two, frame adhesive precedes internal connection and LC one drop fill. Then silicon die and ITO glass die are laminated before frame adhesive cure. Afterwards die mount, wire bonding and encapsulation come last.

This application claims priority to Taiwan Patent Application No.104143705 filed on Dec. 25, 2015.

CROSS-REFERENCES TO RELATED APPLICATIONS

Not applicable.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a method of unit level liquid crystaldisplay device assembly process, and more specifically, the presentinvention relates to a method of unit level liquid crystal displaydevice assembly process for liquid crystal on silicon (LCOS).

Descriptions of the Related Art

As shown in FIG. 1, a conventional method of a liquid crystal displaydevice assembly process for liquid crystal on silicon is provided,including following steps: cleaning silicon wafer and glass substrate101; coating an alignment layer 102; coating frame adhesive 103;laminating the silicon wafer and the glass substrate 104; sawing thesilicon wafer and the glass substrate which are singulated into cells bycell singulation 105; filling the cell with liquid crystal in a vacuumchamber 106; sealing a liquid crystal fill port 107; mounting 108;bonding wire 109; and encapsulating 120. FIG. 2 is another conventionalmethod, including following steps: cleaning silicon wafer and glasssubstrate 201; coating alignment layers 202; coating frame adhesive 203;internal connecting glass substrate electrically 204; filling withliquid crystal by one drop filling (ODF) process 205; laminating thesilicon wafer and the glass substrate into a laminated body 206; sawingthe laminated body into cells 207; mounting 208; bonding wire 209; andencapsulating 210.

However, the prior art is not suitable for same set of equipment indifferent wafer size process (6-in, 8-in, or 12-in). For example, in theoblique evaporation process for coating alignment layer, the bigger thewafer size is, the bigger the vacuum deposition system requires.Therefore, coating alignment layer will take more time. Additionally, itwill also take more time to fill with liquid crystal because of a biggerwafer size. Furthermore, because the prior art is applied to a wholewafer, the good bare dies cannot be picked in early step of process, thebad bare dies are also processed with good bare dies, thus it will takea lot of unnecessary expense. And the bond pad of the prior art is onlyon one of the two scribe and break areas. Further, the development timeis longer because the cycle time of the process of the prior art is toolong. And the circuit board of the liquid crystal module cannot befabricated earlier than the liquid crystal assembly process.

The present invention is, therefore, arisen to obviate or at leastmitigate the above mentioned disadvantages.

SUMMARY OF THE INVENTION

Accordingly, the present invention provides a method of unit levelliquid crystal display device assembly process for liquid crystal onsilicon (LCOS), which is unrestricted by the wafer size. The same set ofequipment is suitable for different wafer size process (6-in, 8-in, or12-in). For example, in the oblique evaporation process for coatingalignment layer, the same vacuum deposition system can be used indifferent wafer-size process. And because the unit level die aftersawing are much smaller than the wafer, the required volume of thevacuum chamber is much smaller. Therefore, coating alignment layer willtake less time. Furthermore, because the good bare dies are picked inearly step of process, it will not take a lot of unnecessary expense onthe bad dies. Additionally, filling with liquid crystal will not becomplicated because the process condition (parameter, size . . . etc) ofthe unit level dies after sawing is consistent. And the bond pad can beput on any side of the four sides. In addition, the development time isreduced because the cycle time of the present invention is much shorter.And the circuit board of the liquid crystal module can be fabricatedearlier than the liquid crystal display device assembly process.

Specifically, the present invention provides a method of unit levelliquid crystal display device assembly process for LCOS. The maincomponents of this invention are the die carrier and process apparatus,in which the carrier uses a process similar to wafer level fan-outpackaging process, as one of the important technical features. Thecarrier has an individual LCOS cell carrier sequence, can carry adifferent number of dies, and ensure that each individual die can belocated with an accurate orientation to carry out liquid crystal displaydevice assembly process. Every time, after the liquid crystal displaydevice assembly process is completed, all carriers will be cleaned inorder to make the next batch of LCOS cell. In some embodiments of thepresent invention, the carrier can also have lateral arm or backsidevacuum jack to hold the dies.

Specifically, in some embodiments of the present invention, a method ofunit level liquid crystal display device assembly process for liquidcrystal on silicon includes the following steps: sawing a silicon waferand an ITO glass substrate into a plurality of silicon dies and aplurality of ITO glass dies respectively; cleaning the silicon dies andthe ITO glass dies; picking one said silicon die and one said ITO glassdie from the plurality of silicon dies and the plurality of ITO glassdies; coating a first alignment layer and a second alignment layer onthe silicon die and the ITO glass die respectively; coating frameadhesive on the silicon die and laminating the silicon die and the ITOglass die; then frame adhesive cure. Subsequently pick suitable LCOScell from the carrier, and fill with liquid crystal in vacuum chamber.After end seal the liquid crystal fill port, mounting the silicon dieonto an external circuit board; bonding a wire between the silicon dieand the external circuit board to electrically connect the silicon dieand the external circuit board; and electrically connecting the externalcircuit board with the ITO glass die with an external electricalconductive material. In some embodiments of the present invention, theframe adhesive is applied on the ITO glass die. Besides, the silicon dieand the glass die are separately transferred to carriers after pickingstep for alignment layer coating. In some embodiments of the presentinvention, the first alignment layer used the same alignment materialand process as the second alignment layer, that is, both first andsecond alignment layers are the same alignment layer. In someembodiments of the present invention, the first alignment layer isdifferent with the second alignment layer.

Furthermore, in some embodiments of the present invention, a method ofunit level liquid crystal display device assembly process for liquidcrystal on silicon includes the following steps: sawing a silicon waferand an ITO glass substrate into a plurality of silicon dies and aplurality of ITO glass dies respectively; cleaning the silicon dies andthe ITO glass dies; picking one said silicon die and one said ITO glassdie from the plurality of silicon dies and the plurality of ITO glassdies; coating a first alignment layer and a second alignment layer onthe silicon die and the ITO glass die respectively; coating frameadhesive on the silicon die; connecting the silicon die with an internalelectrical conductive material; filling with liquid crystal; laminatingthe ITO glass die and the silicon die, wherein the silicon die and theITO glass die are electrically connected via the internal electricalconductive material, the internal electrical conductive material islocated between the silicon die and the ITO glass die; curing the frameadhesive; mounting the silicon die onto an external circuit board; andbonding a wire between the silicon die and the external circuit board toelectrically connect the silicon die and the external circuit board. Insome embodiments of the present invention, the frame adhesive is appliedon the silicon die; and in some embodiments of the present invention,the frame adhesive is applied on the ITO glass die. Besides, the silicondie and the glass die are separately transferred to carriers afterpicking step. In some embodiments of the present invention, the firstalignment layer used the same alignment material and process as thesecond alignment layer, that is, both first and second alignment layersare the same alignment layer. In some embodiments of the presentinvention, the first alignment layer is different with the secondalignment layer.

The present invention will be more fully understood in view of thefollowing description and drawings. Other objectives and advantages ofthe present invention will be described with reference to the followingdescription and the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a liquid crystal display device assembly process inaccordance with a first embodiment of the prior art.

FIG. 2 illustrates a liquid crystal display device assembly process inaccordance with a second embodiment of the prior art.

FIG. 3 illustrates a liquid crystal display device assembly process inaccordance with a first embodiment of the present invention.

FIG. 4 illustrates a liquid crystal display device assembly process inaccordance with a second embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 3 shows a liquid crystal display device assembly process 300 inaccordance with one embodiment of the present invention. Specifically,FIG. 3 which illustrates a method of unit level liquid crystal displaydevice assembly process for liquid crystal on silicon, including thefollowing steps.

A silicon wafer and an ITO glass substrate are sawed into a carrier ofsilicon dies and a carrier of ITO glass dies respectively 301.Furthermore, the silicon die and the ITO glass die are sawed in unitlevel so as to be assembled into a LCOS (Liquid Crystal On Silicon)cell. For example, a LCOS panel with a 720P resolution, which is singlepanel field sequential color LCOS with digital drive, consists of1280×720 pixel array of 6.4×6.4-um square dot size, 0.37-in of activedisplay diagonal size, and package size of 7.75-mm width×25.4-mm length.The “unit level” may refer to the LCOS cell with an active area of0.37-in in diagonal size, so that the silicon die and ITO glass die aremuch smaller than the silicon wafer and the glass substrate (6, 8 or 12inch).

Next, the silicon dies and the ITO glass dies are cleaned 302.

Then, one said silicon die and one said ITO glass die are picked fromthe plurality of silicon dies and the plurality of ITO glass diesrespectively 303. Moreover, in this step 303, only the good silicon dieand the good ITO glass die are picked and used in following step toavoid performing extra process on the bad dies, so that, the cost willbe reduced. Next, the silicon die and the ITO glass die are separatelytransferred to carriers after picking step 303. Wherein each saidcarrier has an array of cells with each cell placed in an individualcell cavity formed on the carriers. Each said cell cavity ensures thateach individual silicon die or ITO glass die can be placed with anaccurate orientation to carry out liquid crystal display device assemblyprocess. In some embodiments, each said cell cavity further has sidearms or vacuum jack from the back to hold the silicon die or the ITOglass die.

Then, a first alignment layer and a second alignment layer are coated onthe silicon die and the ITO glass die respectively 304. Specifically,the first alignment layer and the second alignment layer are coated on afirst conductive layer on the silicon die display active area and asecond electrical layer on the ITO glass die display active arearespectively. In some embodiments of the present invention, the firstalignment layer used the same alignment material and process as thesecond alignment layer, that is, both first and second alignment layersare the same alignment layer. In some embodiments of the presentinvention, the first alignment layer is different with the secondalignment layer.

Then, frame adhesive is coated on the silicon die 305 (in someembodiments, the frame adhesive may be coated on the ITO glass die), andthe silicon die and the ITO glass die are laminated into a laminatedcell 306. In this step 305, one of the silicon die and the ITO glass diewhich is placed on the carrier should be transferred to another carrierto laminate.

Next, the frame adhesive is cured 307. Wherein, the frame adhesive, thefirst alignment layer and the second alignment layer enclose a liquidcrystal chamber. And the liquid crystal chamber has a fill port.

Then, the laminated cell is picked from the carrier 308.

Next, the liquid crystal chamber of the laminated cell is filled withliquid crystal in vacuum chamber via the fill port 309 and the fill portis sealed 310, so that the laminated cell becomes a LCOS cell.

Then, the silicon die is mounted onto an external circuit board 311.

Next, a wire is bonded between the silicon die and the external circuitboard to electrically connect the silicon die and the external circuitboard 312.

Then, an encapsulating process is performed 313.

Next, the external circuit board is electrically connected with the ITOglass die 314 with an external conductive material.

FIG. 4 shows a liquid crystal display device assembly process 400 inaccordance with one embodiment of the present invention. Specifically,FIG. 4 illustrates a method of unit level liquid crystal display deviceassembly process for liquid crystal on silicon, including the followingsteps.

A silicon wafer and an ITO glass substrate are sawed into a plurality ofsilicon dies and a plurality of ITO glass dies respectively 401. TheSilicon wafer and the ITO glass are mounted on a tape respectively priorto sawing step 401. Then, both silicon dies on wafer tape and ITO glassdies on wafer tape are subjected to a cleaning step 402 to ensure thecleanliness of the silicon dies and the ITO glass dies. Next, the goodsilicon die and the good ITO glass die are picked 403 and separatelytransferred to different carriers. Wherein each said carrier has anarray of cell cavities to carry a different number of dies, and eachsaid cell cavity ensures that each individual silicon die or ITO glassdie can be located with an accurate orientation to carry out alignmentlayer coating process. In some embodiments, each said cell cavityfurther has side arms or vacuum jack from the back to hold the silicondie or the ITO glass die.

Next, a first alignment layer and a second alignment layer are coated onthe silicon die and the ITO glass die respectively 404. In someembodiments of the present invention, the first alignment layer used thesame alignment material and process as the second alignment layer, thatis, both first and second alignment layers are the same alignment layer.In some embodiments of the present invention, the first alignment layeris different with the second alignment layer.

After alignment layer coating step, the silicon die and the ITO glassdie should be placed on the same carrier.

Then, frame adhesive is coated on the silicon die or the ITO glass die405.

Next, one of the silicon die and the ITO glass die is connected with aninternal electrical conductive material 406.

Then, liquid crystal is filled 407. Moreover, the liquid crystal isfilled by One Drop Fill (ODF) process.

Next, the silicon die and the ITO glass die are laminated 408. Wherein,the ITO glass die is adhered to the silicon die by frame adhesive, thesilicon die and the ITO glass die are electrically connected via theinternal electrical conductive material, the internal electricalconductive material is located between the silicon die and the ITO glassdie. More specifically, the internal electrical conductive material iselectrically connected with a first conductive layer on the silicon dieand a second electrical layer on the ITO glass die respectively.

Then, the frame adhesive is cured 409.

Next, the silicon die is mounted onto an external circuit board 410.

Then, a wire is bonded between the silicon die and the external circuitboard to electrically connect the silicon die and the external circuitboard 411.

Next, an encapsulating process is performed 412.

In the embodiments of FIGS. 3-4, the first alignment layer or the secondalignment layer is coated by an oblique evaporation process(SiO_(x)/SiO₂ process). In a high vacuum chamber, SiO_(x) or SiO₂ (orother inorganic material) is thermally evaporated and forming SiOcolumnar bodies on the silicon die or ITO glass die in a specific angle,so that the angle or the density of the alignment layer can becontrolled precisely.

The first alignment layer or the second alignment layer may be coated bya polyimide (PI) rubbing process. First, a polyimide (PI) layer iscoated on the silicon die or the ITO glass die. Then, a rubbing rollrolls on the PI layer to arrange main chains of PI in a specificdirection. The PI rubbing process can be performed in room temperatureand a mature process for mass production.

The first alignment layer or the second alignment layer may be coated bya photo alignment process. A photo alignment layer containingstructurally anisotropic polymers is formed. UV rays are irradiated tothe photo alignment layer to arrange main chains of the structurallyanisotropic polymers in a specific direction. The structurallyanisotropic polymers may be Cyclic Olefin Copolymers. The main chains ofthe Cyclic Olefin Copolymers have good characteristics ofphotosensitivity, photo alignment, alignment property, and thermalstability.

The first alignment layer or the second alignment layer may be coated byan ink-jet printing process to form at least one polymer layer withdefined thickness. Because the ink-jet printing process is contactless,the alignment layer can be more smooth and homogeneous. Additionally,the ink-jet printing process can use material efficiently and reducewaste.

In some embodiments of the present invention, the external circuit boardis located on a frame edge of a LCOS panel, a light mask on a topsurface of the ITO glass die may be fabricated by an ink-jet printingprocess to reduce phenomenon of reflecting or scattering, so thatoptical contrast of the LCOS panel will be higher. Furthermore, thelight mask is a light absorbing mask, which is able to absorb and avoidlight from scattering or reflecting.

Besides, a predetermined picture or photo resist can be coated preciselyby software, instead of preparing another expensive mask, so that thecost can be reduced. In addition, if there are at least two spraynozzles on each equipment (for alignment layer or light mask), the moredies can be coated at the same time, so that the efficiency ofproduction can rise.

In some embodiments of the present invention, the first alignment layeror the second alignment layer may be coated by a chemical vapordeposition process in a vacuum chamber. First, the die is put in thevacuum chamber. Then, the vacuum chamber is purged and then filled withan inert gas to reduce water vapor. Next, the liquid crystal alignmentlayer is coated by using vapor deposition of a silane material. Thesilane material may be Perfluorooctyltriethoxsilane,Octyltriethoxysilane, Trimethylsiyldiethylamine or Trichlorosilane.Furthermore, the chemical vapor deposition process may be aplasma-enhanced chemical vapor deposition process. By using thisprocess, multiple dies can be placed in the chamber together to coatalignment layers simultaneously. Thus, the processes can produce verythin liquid crystal alignment layers at a high production rate.

As will be appreciated by those skilled in the art, the presentinvention is not limited to the detailed descriptions of the embodimentsdisclosed above, but may also be embodied in other specific formswithout departing from the spirits of the present invention. Theembodiments are provided only for purpose of illustration but not forlimitation, and the present invention shall be governed by the claimsbut not by the aforesaid descriptions. All variations made within thespirits of the claims and equivalents thereof shall all be coveredwithin the scope of the present invention.

What is claimed is:
 1. A method of unit level liquid crystal displaydevice assembly process for liquid crystal on silicon, including thefollowing steps: sawing a silicon wafer and an ITO glass substrate intoa plurality of silicon dies and a plurality of ITO glass diesrespectively; cleaning the silicon dies and the ITO glass dies; pickingone said silicon die and one said ITO glass die from the plurality ofsilicon dies and the plurality of ITO glass dies respectively; coating afirst alignment layer and a second alignment layer on the silicon dieand the ITO glass die respectively; coating frame adhesive on thesilicon die or the ITO glass die; curing the frame adhesive, wherein theframe adhesive, the first alignment layer and the second alignment layerenclose a liquid crystal chamber, and the liquid crystal chamber has afill port; filling the liquid crystal chamber with liquid crystal viathe fill port and sealing the fill port; mounting the silicon die ontoan external circuit board; bonding a wire between the silicon die andthe external circuit board to electrically connect the silicon die andthe external circuit board; and electrically connecting the externalcircuit board with the ITO glass die with an external conductivematerial.
 2. The method of claim 1, wherein the first alignment layer orthe second alignment layer is coated by one of a polyimide rubbingprocess, an oblique evaporation process, a photo alignment process andan ink-jet printing process.
 3. The method of claim 1, wherein the firstalignment layer or the second alignment layer is coated by a chemicalvapor deposition process in a vacuum chamber.
 4. The method of claim 3,wherein the chemical vapor deposition process is a plasma-enhancedchemical vapor deposition process.
 5. The method of claim 1, furtherincluding a following step: fabricating a light mask on a top surface ofthe ITO glass die by an ink-jet printing process.
 6. The method of claim1, wherein the silicon die and the ITO glass die are separatelytransferred to carriers after picking step.
 7. The method of claim 6,wherein each said carrier has an array of cell cavities, each said cellcavity has precise dimension to hold one said silicon die or one saidITO glass die.
 8. The method of claim 7, wherein the cell cavity furtherhas side arms to hold the silicon die or the ITO glass die.
 9. Themethod of claim 1, further including a following step between the stepof bonding a wire between the silicon die and the external circuit boardand the step of electrically connecting the external circuit board withthe ITO glass die: performing an encapsulating process.
 10. A method ofunit level liquid crystal display device assembly process for liquidcrystal on silicon, including the following steps: sawing a siliconwafer and an ITO glass substrate into a plurality of silicon dies and aplurality of ITO glass dies respectively; cleaning the silicon dies andthe ITO glass dies; picking one said silicon die and one said ITO glassdie from the plurality of silicon dies and the plurality of ITO glassdies respectively; coating a first alignment layer and a secondalignment layer on the silicon die and the ITO glass die respectively;coating frame adhesive on the silicon die or the ITO glass die;connecting one of the silicon die and the ITO glass die with an internalelectrical conductive material; filling with liquid crystal; laminatingthe ITO glass die and the silicon die, wherein the ITO glass die isadhered to the silicon die by frame adhesive, the silicon die and theITO glass die are electrically connected via the internal electricalconductive material, the internal electrical conductive material islocated between the silicon die and the ITO glass die; curing the frameadhesive; mounting the silicon die onto an external circuit board; andbonding a wire between the silicon die and the external circuit board toelectrically connect the silicon die and the external circuit board. 11.The method of claim 10, wherein the first alignment layer or the secondalignment layer is coated by one of a polyimide rubbing process, anoblique evaporation process, a photo alignment process and an ink-jetprinting process.
 12. The method of claim 10, wherein the firstalignment layer and the second alignment layer is coated by a chemicalvapor deposition process in a vacuum chamber.
 13. The method of claim12, wherein the chemical vapor deposition process is a plasma-enhancedchemical vapor deposition process.
 14. The method of claim 10, furtherincluding a following step: fabricating a light mask on a top surface ofthe ITO glass die by an ink-jet printing process.
 15. The method ofclaim 10, wherein the silicon die and the ITO glass die are separatelytransferred to different carriers after picking step.
 16. The method ofclaim 15, wherein each said carrier has an array of cell cavities, eachsaid cell cavity has precise dimension to hold one said silicon die orone said ITO glass die.
 17. The method of claim 16, wherein the cellcavity further has side arms to hold the silicon die or the ITO glassdie.
 18. The method of claim 10, further including a following stepafter the step of bonding the wire between the silicon die and theexternal circuit board: performing an encapsulating process.